1. Field of the Invention
The invention relates to an apparatus and method for controlling fan operation.
2. Background of the Related Art
FIG. 1 is a block diagram of an apparatus for controlling a fan operation in a portable device. As shown in FIG. 1, the apparatus includes an input unit 11 (for example, a keyboard), a fan 14 for blowing and heating/cooling operations, a temperature sensor 12 for detecting system temperature, a power supply 13, and a microcomputer 10 connected to the above elements to control on/off operations of the fan 10 by using the detected temperature. Since a portable device, such as a notebook computer, generates a large amount of heat, the fan is used to remove the heat.
When the notebook is in a power-on state, a large amount of heat is generated even when the notebook works little or does not work, so that the fan is operated periodically. That is, the fan repeats a stop operation and a temporary rotation operation. If the fan is rotated depending on the above operation mode, an amount of heat is rapidly removed so that an internal temperature of the notebook computer falls to some degree.
FIG. 2 illustrates a control state of the fan operation. As shown in FIG. 2, the fan operation of the notebook computer is controlled by pulse width modulation (PWM), which is dependent on states of peripheral devices. That is, the fan repeats a normal operation, a stop operation, and a spin-up operation. The spin-up operation is an operation that allows the fan to rotate at a speed higher than a normal speed.
In the case of the normal operation, for example, ˜2500 rpm, a value corresponding to a hexadecimal value of 0×25 is set to firmware program of the microcomputer. In the case of the spin-up operation, for example, ˜3500 rpm, a value corresponding to a hexadecimal value of 0×2C is set to firmware program of the microcomputer. That is, if PWM duty is larger, the fan rotates at a high speed. Meanwhile, if PWM duty is smaller, the fan rotates at a low speed.
When the fan starts to rotate from a stop state, the PWM duty is momentarily increased larger than the PWM duty of the normally rotating fan. At this point, the duration time (about 1 second) is called “SpinUp Time”. When the fan starts to rotate, the PWM duty is set normally.
In the case where the stopped fan is rotated, if the PWM duty of the normal fan speed is applied, the fan may not be rotated due to characteristics of the fan. Therefore, the fan is rotated during a predefined duration time according to the spin-up operation.
In this case, however, the user may hear severe noise. That is, the noise of the fan is relatively increased due to the periodic rotation and stop operations. In addition, when the stopped fan starts to rotate, the PWM duty is increased due to the spin-up operation and thus the fan rotates almost instantaneously at a high speed. The noise occurring at that time is relatively large. Further, the fan operation does not change depending on the specific operation state of the system.